1. Field of the Invention
The present invention relates to a wireless mobile communication system and, more particularly, to a method for implementing transmit diversity in a wireless mobile communication system adopting a Single Carrier-Frequency Division Multiple Access (SC-FDMA) scheme.
2. Discussion of the Related Art
Conventionally, a single Transmit (Tx) antenna and a single Receive (Rx) antenna are used. Multi-Input Multi-Output (MIMO) uses a plurality of Tx antennas and a plurality of Rx antennas to thereby increase the transmission and reception efficiency of data. That is, the use of multiple antennas at both a transmitter and a receiver may increase capacity and performance in a wireless communication system. Hereinbelow, MIMO may be referred to as ‘multi-antenna’.
The multi-antenna technology does not depend on a single antenna path to receive a whole message. Rather, it completes the data by combining data fragments received through a plurality of antennas. With the multi-antenna technology, data rate may be increased within a cell area of a certain size, or system coverage may be extended with a predetermined data rate ensured. Furthermore, this technology may find its use in a wide range including mobile terminals, relays, etc. The multi-antenna technology may overcome transmission capacity problems encountered with the conventional single-antenna technology.
FIG. 1 illustrates the configuration of a typical MIMO communication system. Referring to FIG. 1, a transmitter has NT Tx antennas and a receiver has NR Rx antennas. The use of a plurality of antennas at both the transmitter and the receiver increases a theoretical transmission capacity, compared to the use of a plurality of antennas at only one of the transmitter and the receiver. The channel transmission capacity increases in proportion to the number of antennas. Hence, the transmission rate and the frequency efficiency may be increased. Given a maximum transmission rate Ro in case of a single antenna, the transmission rate may be increased, in theory, to the product of Ro and Ri in case of multiple antennas, where Ri is an increase rate of the transmission rate.
For instance, a MIMO communication system with four Tx antennas and four Rx antennas may achieve a four-fold increase in transmission rate theoretically, relative to a single-antenna system. Since the theoretical capacity increase of the MIMO system was proved in the middle 1990's, many techniques have been actively studied to increase data rate in real implementation. Some of the techniques have already been reflected in various wireless communication standards for 3rd Generation (3G) mobile communications, future-generation Wireless Local Area Network (WLAN), etc.
There are two types of MIMO schemes: spatial diversity and spatial multiplexing. Spatial diversity increases transmission reliability using symbols that have passed in multiple channel paths, whereas spatial multiplexing increases transmission rate by transmitting a plurality of data symbols simultaneously through a plurality of Tx antennas. The advantages of these two schemes may be taken by using them in an appropriate combination.
Active studies are underway in many respects regarding the MIMO technology, inclusive of studies of information theory related to calculation of multi-antenna communication capacity in diverse channel environments and multiple access environments, studies of measuring radio channels and deriving a model for a MIMO system, studies of time-space signal processing techniques to increase transmission reliability and transmission rate, etc. Especially, it is necessary to conduct a study of a method for efficiently implementing transmit diversity to increase transmission reliability in an SC-FDMA system.